1. Field of the Invention
This invention relates to a grinding method for curved surface of a work having a concave surface such as a spherical surface of a given radius and a concave and curved surface of a bearing groove and an apparatus thereof.
2. Conventional Art
As a working apparatus for carrying out a precision grinding on a spherical surface such as a rod end of a ball joint, there is what is shown in FIG. 4. A configuration of a grindstone 1 is cylindrical as a whole, and at its inner end of the cylinder portion a conical grinding surface 1a of a given width (hereinafter referred to as xe2x80x9ccup grindstonexe2x80x9d) formed by applying a chamfer is formed. The diameter of the cup grindstone 1 and the inclination angle of the conical grinding surface are selected in accordance with a configuration of a work W.
And the cup grindstone 1 is installed in the driving shaft 2 rotating toward a direction of an arrow A (hereinafter referred to as xe2x80x9cthe first driving shaftxe2x80x9d) and the grinding surface 1a is driven to rotate in a circumferential direction. Further, it is provided with a displacing means not shown in which, in a state where a driving shaft 2 is driven to rotate, the grinding surface 1a is made to be displaced toward the direction B.
The work W, as a surface Wa to be worked, has a spherical surface which remains a finishing process to be applied for grinding. Further, the work W has a through hole, which is coupled with and fixed to a driving shaft 3 (hereinafter referred to also as xe2x80x9cthe second driving shaftxe2x80x9d) which is rotated on an axis perpendicular to the first shaft 2 in the direction of arrow C.
And, in a state where the cup grindstone 1 is made to rotate in the direction of arrow A and the work W is made to rotate in the direction of arrow C, the cup grindstone 1 is made to get close to the work W. Then, the total surface (circumference) of the grinding surface 1a abuts to the surface Wa, which is the grinding surface of the work, and generates a three-dimensional relative displacement between the grinding surface 1a of the grindstone 1 and the surface Wa to be ground of the work W. Such three-dimensional relative displacement provides a high precision roundness or surface roughness.
By the way, in the case where a grinding is carried out by not only a cup grindstone 1 but also another grindstone, it is necessary to carry out a dressing on the grinding surface of the work after a given time period of working. This is because fine particles ground by the grindstone grains and the grindstone grains peeled off the grindstone are clogged with the grinding surface. Such clogging becomes more outstanding in proportion to the fineness of the grindstone grain which makes a super precise grinding difficult.
In order to solve the above problem, a dressing method in which the ground working and the dressing process are carried out simultaneously is disclosed in the patent laid open Nos. Hei 1-188266 and Hei 7-1333 and so on. Such dressing method is explained in accordance with FIG. 5. As a grindstone 4, what contains a conductive material is used. Furthers electrodes 5 are disposed opposing each other on the grinding surface 4a of the grindstone 4. Further, a nozzle 6 for applying a conductive coolant on the grinding surface 4a between the electrodes is disposed nearby. And, an electric supply equipment 7 for supplying an electricity to the grindstone 4 is provided on the grindstone 4, which is connected to the electric source not shown.
Now, at the time of grinding a surface Waxe2x80x2 of a work Wxe2x80x2 by rotating the grindstone 4 in the direction of arrow D, the conductive coolant is supplied to the grinding surface 4a and the grinding portion of the electrodes 5 from the nozzle 6 and the electricity is supplied through the electrodes 5 and the electric supply equipment 7, then between the grinding surface 4a and the coolant a voltage is applied to generate an electrolytic effect. Due to this electrolytic effect, the conductive material on the grinding surface 4a is dissolved in the conductive coolants thereby the clogging on the grinding surface 4a is solved.
However, when applying the above dressing method on the spherical surface shown in FIG. 4, since the whole of the grinding surface 1a of the cup grinding stone 1 abuts to the surface Wa to be worked, the electrodes for applying the voltage to the grinding surface 1a could not be provided, in the case of working a spherical surface shown in FIG. 4, a dressing of in-process (an another process within other process) could not be carried out and as a result, there has been a defect that, even though the grain size of the grindstone is high, a desired surface roughness could not be obtained.
Further, in the case where not only the spherical surface working as shown in FIG. 4, but also a curved surface grinding due to generation of three-dimensional relative displacement between the grinding surface of the grindstone and the surface to be ground is carried ground, an arrangement for a complicated surface configuration to be followed by having an electrode followed the displacement of a grindstone has been difficult.
The present invention has been made in the light of the above problem, the purpose of it is to provide a spherical surface having a given radius or a concave surface of a work such as bearing groove with a high precision of roundness or a curved surface.
According to a first aspect of the method for working a curved surface of the present invention, the method is characterized in that, a three-dimensional relative displacement is made to be generated between a grinding surface of an conductive grindstone and a surface of a conductive work to be ground, when carrying out to grind a curved surface, while supplying an conductive coolant to a grinding portion of the work between the conductive grindstone and the conductive work and the work is ground while dressing the conductive grindstone by electrolytic effect.
According to the above invention, by applying a voltage to the grinding portion between the conductive grindstone and the conductive work, since the conductive material of the grindstone is dissolved in the conductive coolant, the clogging of the grinding surface of the conductive grindstone is avoided.
According to a second aspect of the method for working a curved surface of the present invention, whole of the grinding surface of the conductive grindstone is made to be abutted to the surface of the work to be ground, and at the time when grinding a curved surface while generating a three-dimensional relative displacement, a voltage is applied to a grinding portion between the conductive grindstone and a surface to be ground while supplying a conductive coolant thereto and a grinding is carried out while dressing the grindstone by electrolysis.
According to the above aspect of the present invention, in the case where a grinding work is carried out in such a manner as whole of the conductive grindstone abuts to the surface to be ground of the conductive work too, a voltage is applied to a grinding portion between the conductive grindstone and the conductive work and the conductive material on the surface of the conductive grindstone is made to be dissolved in the conductive coolant, thereby the clogging of the surface of the conductive grindstone is solved.
Further, according to a third aspect of an apparatus for working a curved surface of the present invention for solving the above problems, it comprises a driving means to generate a three-dimensional relative displacement between the grinding surface of the conductive grindstone and the surface to be ground of the conductive work, a coolant supplying means to supply the conductive coolant between the grinding surface of the grindstone and the surface to be ground of the conductive work and the electric supply equipment means to supply a current to the conductive grindstone and the conductive work.
According to the above invention, by the above driving means it is made to enable to work a desired curved surface and since a voltage is applied to the conductive grindstone by the above electric supply equipment and the conductive material of the grindstone of the surface of the conductive grindstone is dissolved in the conductive coolant supplied from the above mentioned supplying means, the above clogging of the grinding surface of the conductive grindstone is solved.
In addition, according to a fourth aspect of the curved surface processing apparatus, said conductive grindstone comprises a conical grinding surface, said driving means comprises the first driving shaft to rotate the conical grinding surface of the conductive grindstone in the circumferential direction on an axis perpendicular to the first driving shaft, and a displacement means which makes the first and second driving shafts come to close and separated each other.
According to the above constitution, while solving the clogging of the grinding surface of the conductive grindstone in an in-process, it becomes possible to make the three-dimensional relative displacement generated between the conical grinding surface of the conductive grindstone and the surface to be ground of the conductive work and give the surface to be worked of the conductive work a high precision of roundness or unevenness of the surface.
According to a fifth aspect of a curved surface working apparatus of the present invention, either one or both of the first and second driving shaft comprises a swinging means to swing around a crossing point of the axes of the first and second driving shafts. And, due to the generation of such mutual swinging motion between the first and second driving shafts, without changing the contacting state between the grinding surface 1axe2x80x2 and the surface Wa to ground, the grinding surface 1axe2x80x2 and the surface Wa to be ground in such a manner as it licks the surface.